Symbolizing Your Data with ArcMap

6
Symbolizing your data
IN THIS CHAPTER
• A map gallery
• Drawing all features with one symbol
• Drawing features to show
categories like names or types
• Managing categories
• Ways to map quantitative data
Choosing how to represent your data on a map may be the most important
mapmaking decision you make. How you represent your data determines
what your map communicates.
On some maps, you might simply want to show where things are. The easiest
way to do this is to draw all the features in a layer with the same symbol. On
other maps, you might draw features based on an attribute value or
characteristic that identifies them. For example, you could map roads by type
to get a better sense of traffic patterns or map the wildlife habitat suitability
of a particular bird species, ranked from least to most suitable.
In general, you can draw map features as follows:
• Standard classification schemes
• With a single symbol
• Drawing features to show
quantities like counts or amounts
• To show a category such as a name (unique values maps)
• Setting a classification
• Drawing features to show
multiple attributes
• To represent a quantity such as population (graduated color, graduated
symbol, and dot density maps)
• To show multiple attributes that are related (multivariate and chart maps)
You can also draw these other data types:
• Drawing features with charts
• Images and rasters (see Chapter 14, ‘Working with rasters’)
• Drawing TINs as surfaces
• TINs representing a three-dimensional surface
• Drawing CAD layers
• Advanced symbolization
• CAD drawing files
Browse the map gallery on the next few pages to see the various ways you
can symbolize your data.
133
ch6.p65
133
12/04/2000, 12:09 PM
A map gallery
Single symbol map
Unique values map
Drawing your data with just a single symbol gives you a sense of
how features are distributed—whether they’re clustered or
dispersed—and may reveal hidden patterns.
On a unique values map, you draw features based on an attribute
value, or characteristic, that identifies them. In the map above,
each land use type is drawn with a specific color. Typically, each
unique value is symbolized with a different color. Drawing
features based on unique attribute values shows the following:
In the map above, you can easily see where people live and
conclude that some areas are more densely populated based on
the number of cities clustered together.
•
How similar features are distributed—whether they’re
grouped or dispersed
•
How different feature types are located in relation to each
other
•
How much of one category there is compared to other
categories
134
ch6.p65
USING ARCMAP
134
12/04/2000, 12:09 PM
Graduated color map
Graduated symbol map
When you need to map quantities or amounts of things, you
might choose to use a graduated color map. Graduated color
maps have a series of symbols whose colors change according to
the values of the particular attribute. Graduated color maps are
most useful for showing data that is ranked (for example, 1 to 10,
low to high) or has some kind of numerical progression (for
example, measurements, rates, percentages).
Another way to represent amounts of things is to vary the size of
the symbol a feature is drawn with. The graduated symbol map
above uses a larger symbol to show earthquakes with a larger
magnitude. Like graduated color maps, graduated symbol maps
are most useful for showing rank or progression of values.
However, instead of using color to represent the differences in
values, the size of the symbol varies.
The map above uses different shades of color—in a graduated
color ramp—to represent different amounts of people. Here,
darker shades indicate a greater number of people.
When making a graduated symbol map, it is important to choose
the range of symbol sizes carefully. The largest symbols need to
be small enough that neighboring symbols don’t completely
cover one another. At the same time, the range in size from the
smallest to the largest needs to be great enough that the symbol
for each class is distinct.
SYMBOLIZING
ch6.p65
135
YOUR DATA
135
12/04/2000, 12:10 PM
Multivariate map
Chart map
The maps on the previous pages display one attribute, or
characteristic, of the data—for example, a name or an amount.
Multivariate maps display two or more attributes at the same
time. The map above illustrates the level of human impact on the
natural landscape of Australia. Major habitat types are shown
with unique colors, and the level of disturbance for each habitat
is shown with a graduated symbol. The larger the symbol, the
higher the human impact is on the particular habitat.
Chart maps allow you to symbolize multiple attributes on one
map as well as communicate the relationship among different
attributes. Chart maps display charts—bar and pie charts—over
features. The map above shows you the volume and type of
goods distributed by an exporter throughout Asia.
Pie charts show relationships between parts and the whole and
are particularly useful for showing proportions and ratios. Bar
charts compare amounts of related values and are well suited to
showing trends over time. Stacked bar charts can show both the
relative relationship between data as well as allowing for absolute
comparisons.
136
ch6.p65
USING ARCMAP
136
12/04/2000, 12:10 PM
Density map
Raster map
Mapping the density of features lets you see the patterns of where
things are concentrated. This helps you find areas that require
action or meet some criteria. For example, the map above shows
where the highest concentration of crimes occurs in a city. Using
this map, the city may choose to increase the number of police
patrols in the areas of high density.
Much of the most readily available geographic data is in the form
of rasters. A raster can represent almost any geographic features,
though most rasters you’ll work with in ArcMap will probably be
scanned maps or photographs of the earth’s surface. You might
add an aerial photograph to your map to provide a realistic
background to your other data, or you might use satellite imagery
to add up-to-the-minute information about weather conditions or
flood levels. You can even update your other data by using a
raster as a guide for editing.
One way to map density is with a dot density map. This type of
map symbolizes features using dots drawn inside polygons to
represent a quantity. Each dot represents a specific value. For
example, on the crime map, each dot might represent five
incidents of crime. When creating a dot density map, you specify
how many features each dot represents and how big the dots are.
You may need to try several combinations of amount and size to
see which one best shows the pattern.
SYMBOLIZING
ch6.p65
For more information on displaying raster data, see Chapter 14,
‘Working with rasters’.
137
YOUR DATA
137
12/04/2000, 12:11 PM
Color-shaded relief map
Computer-aided design map
One of the ways you can represent a continuous surface, such as
terrain elevation or temperature gradient, is to display the surface
as a color-shaded relief map. This type of map displays elevation
ranges in graduated colors and shades ridges, valleys, and
hillsides using a simulated light source. The shading adds a
realistic effect that makes the surface look as though you are
viewing it from high above. The combined use of color for
elevation and shading for surface morphology results in a highly
informative, yet easy to interpret, view of your surface.
You can integrate CAD drawings onto your maps seamlessly,
without having to convert these files into other GIS formats. This
is particularly useful if your organization has existing CAD data
resources. For example, some departments in your organization
may be using a CAD package to help manage facilities and other
infrastructure. You can let ArcMap draw these layers as they
appear in the CAD package, or you can precisely control how to
draw them.
138
ch6.p65
USING ARCMAP
138
12/04/2000, 12:11 PM
Drawing all
features with one
symbol
Often, seeing where something
is—and where it isn’t—can tell
you exactly what you need to
know. Mapping the location of
features reveals patterns and
trends that can help you make
better decisions. For example, a
business owner might map where
his customers live. Seeing where
they live can help him decide
where to target his advertising.
The easiest way to see where
features are is to draw them
using a single symbol. You can
draw any type of data this way.
When you create a new layer,
ArcMap by default draws it with
a single symbol.
Tip
Changing the symbol
To quickly change the symbol
features are drawn with, click the
symbol in the table of contents to
display the Symbol Selector.
2
Drawing a layer using a
single symbol
1. In the table of contents, rightclick the layer you want to
draw with a single symbol
and click Properties.
2. Click the Symbology tab.
3
4
3. Click Features.
Because Single symbol is the
only option, ArcMap automatically selects it.
4. Click the Symbol button to
change the symbol.
5. In the Symbol Selector dialog
box, click a new symbol or
change specific properties of
the symbol.
5
6. Click OK on the Symbol
Selector dialog box.
8
7
7. Type a Label for the feature.
The label appears next to the
symbol in the table of
contents.
8. Click OK.
Tip
Changing the color
To quickly change the color of a
symbol, right-click the symbol in
the table of contents to display the
Color Selector.
SYMBOLIZING
ch6.p65
6
139
YOUR DATA
139
12/04/2000, 12:11 PM
Drawing features
to show categories
like names or types
A category describes a set of
features with the same attribute
value. For example, given parcel
data with an attribute describing
land use—for example, residential, commercial, and public
areas—you can use a different
symbol to represent each unique
land use type. Drawing features
this way allows you to see where
features are and what category
they belong to. This can be useful
if you’re targeting a specific type
of feature for some action or
policy. For instance, a city
planner might use the land use
map to target areas for redevelopment.
In general, look for these kinds
of attributes when mapping by
category, or unique value:
•
Attributes describing the
name, type, or condition of a
feature.
•
Attributes containing
measurements or quantities
that are already grouped, for
example, “0–99”, “100–199”.
•
Attributes that uniquely
identify features, for example,
a county name attribute could
be used to draw each county
with a unique color. u
2
Drawing a layer showing
unique values
1. In the table of contents, rightclick the layer you want to
draw showing unique values
and click Properties.
5
3
2. Click the Symbology tab.
3. Click Categories.
ArcMap automatically selects
the Unique values option.
4. Click the Value Field
dropdown arrow and click the
field that contains the values
you want to map.
5. Click the Color Scheme
dropdown arrow and click a
color scheme.
6. Click Add All Values.
6
8 7
Double-click a symbol to
change it.
This adds all unique values to
the list. Alternatively, click the
Add Values button to choose
which unique values to
display.
7. If you want to have more
descriptive labels, click a
label in the Label column and
type a new one.
8. Click OK.
140
ch6.p65
4
USING ARCMAP
140
12/04/2000, 12:11 PM
You can let ArcMap assign a
symbol to each unique value
based on a color scheme you
choose or explicitly assign a
specific symbol to a specific
attribute value.
To draw features with specific
symbols, you need to create a
style beforehand that contains
symbols named after the attribute
value they represent. For
example, if you have a dataset
that categorizes roads as either
major or minor, then you would
need to have line symbols within
that style named “major” and
“minor”. ArcMap will match the
attribute value to the line symbol
name to draw the feature.
Features that don’t have a
matching line symbol won’t be
drawn. This way of drawing
features is especially useful if
you want to draw your data the
same way on different maps.
2
Drawing features by
referencing specific
symbols in a style
1. In the table of contents, rightclick the layer you want to
draw showing unique values
and click Properties.
5
6
3
4
2. Click the Symbology tab.
3. Click Categories.
4. Click Match to symbols in a
style.
5. Click the Value Field
dropdown arrow and click the
field that contains the values
you want to map.
6. Click the Match to symbols in
Style dropdown arrow and
click the style that contains
symbol names that match
attribute values.
7
89
If the style is not loaded, click
the Browse button to browse
for it on disk.
7. Click Match Symbols.
See Also
For more information on creating
styles, see Chapter 9, ‘Working
with styles and symbols’.
This adds all unique values
that have a matching symbol
in the style. Alternatively, click
the Add Values button to
choose which unique values
to display.
8. If you want to have more
descriptive labels, click a
label in the Label column and
type a new one.
9. Click OK.
SYMBOLIZING
ch6.p65
141
YOUR DATA
141
12/04/2000, 12:11 PM
Tip
Sorting unique values
Ordering unique value
headings
You can also arrange the headings
for unique values. Just select a
heading and use the arrow keys to
move it.
1. In the table of contents, rightclick the layer whose unique
values you want to sort and
click Properties.
2
3
2. Click the Symbology tab.
3. Click the Value column to
show a context menu.
4
4. Click Reverse Sorting.
5. Click OK.
5
Ordering unique values
2
1. In the table of contents, rightclick the layer whose unique
values you want to reorder
and click Properties.
2. Click the Symbology tab.
3. Click the value you want to
move up or down in the list.
4
4. Use the up and down arrows
to either promote or demote
the value in the list.
3
The arrow buttons only move
values within a heading.
5. Click OK.
5
142
ch6.p65
USING ARCMAP
142
12/07/2000, 8:29 AM
If you’re drawing features by
category, the number of categories you display will affect what
patterns are revealed on the map.
Most people can easily discern
up to seven categories for a given
layer. The more technical the
audience, the more categories
they will be able to identify and
the more easily they will be able
to interpret complex patterns.
Conversely, a less technical
audience may benefit more from
a map with fewer categories.
When displaying your data, you
can control how you organize
and display categories for a layer.
If you want to display fewer
categories, you can combine
similar categories into one
category—for example, combine
two detailed land use categories
into a more general one. Combining categories in this manner can
make the patterns more apparent.
However, the trade-off is that
some information may be lost.
Instead of reducing the number
of categories, you might organize
individual categories into groups
that you define. This allows you
to work with and view them as a
group. Additionally, a map reader
will see the groups listed in the
table of contents.
SYMBOLIZING
ch6.p65
2
Combining two or more
categories into one
Managing
categories
1. In the table of contents, rightclick the layer drawn with
unique values for which you
want to combine categories
and click Properties.
2. Click the Symbology tab.
You should already see
categories in the scrolling list.
If you don’t, follow the steps
for ‘Drawing a layer showing
unique values’ in this chapter.
3
4
3. Click the first value you want
to combine. Hold down the
Shift or Ctrl key and click the
additional values that you
want to combine.
5
4. Right-click over the values
and click Group Values.
The selected values will now
be combined into one
category.
5. Click OK.
Splitting up combined
categories
2
1. Right-click a combined
category.
2. Click Ungroup Values.
143
YOUR DATA
143
12/04/2000, 12:12 PM
Tip
Deleting groups
ArcMap will automatically delete
groups that contain no attribute
values in them.
Tip
Renaming groups
Click the group heading in the
table of contents and type a new
name.
2
Organizing categories in
groups
1. In the table of contents, rightclick the layer drawn with
unique values for which you
want to organize categories
and click Properties.
2. Click the Symbology tab.
You should already see
categories in the scrolling list.
If you don’t, follow the steps
for ‘Drawing a layer showing
unique values’ in this chapter.
3
3. Click the first value you want
to group together. Hold down
the Shift or Ctrl key and click
the additional values that you
want to group.
4. Right-click a selected value,
point to Move to Heading,
and click New Heading.
5. Type a name for the new
heading.
7
4
6
5
6. Click OK.
7. Click OK on the Layer
Properties dialog box.
A new heading now appears
in the table of contents with
values grouped in it.
144
ch6.p65
USING ARCMAP
144
12/04/2000, 12:12 PM
Ways to map quantitative data
Quantitative data is data that describes features in terms of a
quantitative value measuring some magnitude of the feature.
Unlike categorical data, where features are described by a unique
attribute value such as a name, quantitative data generally
describes counts or amounts, ratios, or ranked values. For
example, data representing precipitation, population, and habitat
suitability can all be mapped quantitatively.
Which quantitative value should you map?
Knowing what type of data you have and what you want to show
will help you determine what quantitative value to map. In
general, you can follow these guidelines:
•
•
•
Map counts or amounts if you want to see actual measured
values as well as relative magnitude. Use care when mapping
counts as the values may be influenced by other factors and
could yield a misleading map. For example, when making a
map showing the total sales figures of a product by state, the
total sales figure is likely to reflect the differences in
population among the states.
Map ratios if you want to minimize differences based on the
size of areas or numbers of features in each area. Ratios are
created by dividing two data values and are also referred to as
normalizing the data. For example, dividing the 18- to 30year-old population by the total population yields the
percentage of people aged 18–30. Similarly, dividing a value
by the area of the feature yields a value per unit area, or
density.
Map ranks if you’re interested in relative measures and actual
values are not important. For example, you may know a
feature with a rank of “3” is higher than one ranked “2” and
lower than a “4”, but you can’t tell how much higher or lower.
SYMBOLIZING
ch6.p65
Should you map individual values or group them
in classes?
When you map quantitative data, you can either assign each value
its own symbol or group values into classes using a different
symbol for each class.
If you’re only mapping a few values (less than 10), you can
assign a unique symbol to each value. This may present a more
accurate picture of the data, since you’re not predetermining
which features are grouped together. More likely, your data
values will be too numerous to map individually and you’ll want
to group them in classes, or classify the data. A good example of
classified data is a temperature map you might find in a
newspaper. Instead of displaying individual temperatures, these
maps show temperature bands, where each band represents a
given range in temperature.
Ways to classify your data
How you define the class ranges and breaks—the high and low
values that bracket each class—will determine which features fall
into each class and thus what the map will look like. By changing
the classes you can create very different-looking maps. Generally,
the goal is to make sure features with similar values are in the
same class.
Two key factors for classifying your data are the classification
scheme you use and the number of classes you create. If you
know your data well, you can manually define your own classes.
Alternatively, you can let ArcMap classify your data using
standard classification schemes. The four most common schemes
are natural breaks, quantile, equal interval, and standard
deviation. These are described on the following pages.
145
YOUR DATA
145
12/04/2000, 12:12 PM
Standard classification schemes
Natural breaks (Jenks)
Number of features
Classes are based on natural groupings of data values. ArcMap identifies break points by looking for groupings and patterns inherent in
the data. The features are divided into classes whose boundaries are set where there are relatively big jumps in the data values.
Value
Quantile
Number of features
Each class contains an equal number of features. A quantile classification is well suited to linearly distributed data. Because features are
grouped by the number in each class, the resulting map can be misleading. Similar features can be placed in adjacent classes, or features
with widely different values can be put in the same class. You can minimize this distortion by increasing the number of classes.
Value
146
ch6.p65
USING ARCMAP
146
12/04/2000, 12:12 PM
Equal interval
Number of features
This classification scheme divides the range of attribute values into equal-sized subranges. For example, if features have attribute values
ranging from 0 to 300 and you have three classes, each class represents a range of 100 with class ranges of 0–100, 101–200, and 201–
300. This method emphasizes the amount of an attribute value relative to other values, for example, to show that a store is part of the
group of stores that made up the top one-third of all sales. It’s best applied to familiar data ranges such as percentages and temperature.
Value
Standard deviation
Number of features
This classification scheme shows you the amount a feature’s attribute value varies from the mean. ArcMap calculates the mean value
and then generates class breaks by successively adding to it or subtracting from it the standard deviation. A two-color ramp helps
emphasize values above (shown in blue) and below (shown in red) the mean.
Value
SYMBOLIZING
ch6.p65
147
YOUR DATA
147
12/04/2000, 12:13 PM
Drawing features
to show quantities
like counts or
amounts
Representing quantity
with color
When you want your map to
communicate how much of
something there is, you need to
draw features using a quantitative
measure. This measure might be
a count; a ratio such as a
percentage; or a rank such as
high, medium, and low.
2. Click the Symbology tab.
You can represent quantities on a
map by varying the color or
symbol size you use to draw
features. For example, you might
use increasingly darker shades of
blue to represent increasingly
higher rainfall amounts or larger
circles to represent cities with
larger populations.
Generally, you’ll need to classify
your data when you display it.
Classifying data groups features
with similar values into discrete
classes and displays them with
the same symbol. You can either
manually define classes or apply
one of the standard classification
schemes to do so automatically—
just specify the number of classes
you want to show. Once you’ve
defined the classes, you can add
more classes, delete classes, or
redefine class ranges. u
1. In the table of contents, rightclick the layer you want to
draw showing a quantitative
value and click Properties.
24 5 6
3
3. Click Quantities.
ArcMap automatically selects
Graduated colors.
4. Click the Value dropdown
arrow and click the field that
contains the quantitative
value you want to map.
5. To normalize the data, click
the Normalization dropdown
arrow and click a field.
Right-click over a class
to see additional options
such as sorting and
number formatting.
ArcMap divides this field into
the Value to create a ratio.
6. Click the Color Ramp
dropdown arrow and click a
ramp to display data with.
7. Click the Classes dropdown
arrow and click the number of
classes you want.
W
9
8. Click Classify.
9. In the Classification dialog
box, click the Method
dropdown arrow and click the
classification method you
want.
10.Click OK on the Classification
dialog box.
11. Click OK on the Layer
Properties dialog box.
Q
148
ch6.p65
7 8
USING ARCMAP
148
12/04/2000, 12:13 PM
It’s always a good idea to
examine your data before you
map it. For instance, you may
find that you have a few extremely high or low values or
null values where no data is
available. These values can skew
a classification and thus the
patterns on the map. Fortunately,
you can choose to exclude these
values before you classify your
data.
You may also want to normalize
your data before you map it.
When you normalize data, you
divide it by another attribute to
come up with a ratio. Often,
ratios are easier to understand
than the raw data values. For
example, dividing total population by area yields the number of
people per unit area, or a density.
Dividing a store’s sales figure by
the total sales for all stores yields
a percentage of sales at that store.
See Also
For more information on creating
and managing styles, see
Chapter 9, ‘Working with styles
and symbols’.
2
Creating your own color
ramp for a layer
1. In the table of contents, rightclick the layer that shows a
quantitative value and click
Properties.
3
2. Click the Symbology tab.
3. Click Quantities.
4. Double-click the top symbol
in the list and set the start
color for the ramp.
4
6
5
5. Double-click the bottom
symbol and set the end color.
6. Optionally, double-click any
middle symbol to set its color.
Q
This lets you create a
multicolor ramp.
Appearance after the top, middle,
and bottom colors have been set.
7. Click all the middle symbols
you’ve set the color of.
By selecting one or more
middle symbols, the color of
those symbols is included in
the new ramp. Otherwise,
ArcMap only uses the top and
bottom symbols.
8
7
8. Right-click a symbol and click
Ramp Colors.
9. Optionally, right-click the
Color Ramp dropdown and
click Save to save your new
ramp to your default style.
Resulting ramp goes from red to
yellow to green.
You only need to save the
ramp if you want to use it
again on another layer.
9
10.Click OK.
SYMBOLIZING
ch6.p65
149
YOUR DATA
149
12/04/2000, 12:13 PM
Tip
Why don’t the symbols get
bigger when I zoom in?
As you zoom in on the map, the
graduated symbols will not get
bigger. If you want them to get
bigger, you need to set a reference
scale. Right-click the data frame
and click Set Reference Scale. Now
when you zoom in, all the symbols
in the data frame will become
larger.
Tip
With how many digits do
you want to display your
labels?
You can set the number of
significant digits for labels by
clicking the Label column heading.
This reveals a menu that lets you
format the labels.
2
Representing quantity
with graduated symbols
1. In the table of contents, rightclick the layer you want to
draw showing a quantitative
value and click Properties.
2. Click the Symbology tab.
4 5
7 8
3
3. Click Quantities and click
Graduated symbols.
4. Click the Value dropdown
arrow and click the field that
contains the quantitative
value you want to map.
5. To normalize the data, click
the Normalization dropdown
arrow and click a field.
6
ArcMap divides this field into
the Value to create a ratio.
Q
6. Type the minimum and
maximum symbol sizes.
7. Click the Classes dropdown
arrow and click the number of
classes you want.
E
9
8. Click Classify.
9. Click the Method dropdown
arrow and click the classification method you want.
10.Optionally, click Exclusion to
remove unwanted values
from the classification (e.g.,
null values).
11. Click OK on the Classification
dialog box.
W
12.Click OK on the Layer
Properties dialog box.
150
ch6.p65
USING ARCMAP
150
12/04/2000, 12:13 PM
Tip
What’s the difference
between graduated
symbols and proportional
symbols?
When you draw features with
graduated symbols, the quantitative values are grouped into
classes. Within a class, all features
are drawn with the same symbol.
Thus, you can’t discern the value
of individual features; you can
only tell that its value is within a
certain range.
Proportional symbols represent
data values more precisely. The
size of a proportional symbol
reflects the actual data value. For
example, you might map earthquakes using proportional circles,
where the radius of the circle is
based on the magnitude of the
quake. The difficulty with proportional symbols arises when you
have too many values; the symbols
may become indistinguishable.
Also, the symbols for high values
can become so large as to obscure
each other.
The maximum value
symbol is too large
If the symbol for the maximum
value fills the space on the dialog
box, it will probably be too big on
the map. Try reducing the symbol
size for the minimum value,
normalizing the data, or excluding
some values. If it’s still too large,
use graduated symbols instead.
ch6.p65
1. In the table of contents, rightclick the layer you want to
draw showing a quantitative
value and click Properties.
3
2. Click the Symbology tab.
3. Click Quantities and click
Proportional symbols.
4. Click the Value dropdown
arrow and click the field that
contains the quantitative
value you want to map.
6
5. To normalize the data, click
the Normalization dropdown
arrow and click a field.
9
ArcMap divides this field into
the Value to create a ratio.
6. If the Value represents a
measurement on the map—
an area or distance—click the
Unit dropdown arrow and
click a unit. Otherwise, skip to
step 9.
7. Click Square or Circle as the
symbol.
Tip
SYMBOLIZING
2 4 5
Representing quantity
with proportional
symbols
8. Click Radius or Area.
7
For example, click Radius if
your data represents the
distance an earthquake was
felt from its epicenter. Click
Area if the value represents
an area.
9. Click OK.
151
YOUR DATA
151
8
12/04/2000, 12:13 PM
Tip
How big should the dots
be?
When creating a dot density map,
you specify how many features
each dot represents and how big
the dots are. You may need to try
several combinations of amount
and size to see which one best
shows the pattern. In general, you
should select values that ensure the
dots are not so close as to form
solid areas that obscure the
patterns, or so far apart as to
make the variations in density hard
to see.
Representing quantity
with a dot density map
1. In the table of contents, rightclick the layer you want to
draw showing a quantitative
value and click Properties.
2. Click the Symbology tab.
3. Click Quantities and click Dot
density.
2 5 6
4
3
4. Click one or more fields
under Field Selection that
contain the quantitative
values that you want to map.
5. Click the arrow button to add
fields to the field list.
6. Double-click on a dot symbol
in the field list to change its
properties.
7
8 W9
Q
7. Type the dot size or click the
slider to adjust the size.
8. Type the dot value or click the
slider to adjust the value.
9. Check Maintain Density to
preserve the dot density.
When checked, as you zoom
in, the dot size will increase
so that a given area will
visually appear as dense.
Otherwise, the dot size will
remain constant.
10.Optionally, click Properties to
set the dot placement
options.
11. Click OK.
152
ch6.p65
USING ARCMAP
152
12/04/2000, 12:14 PM
Setting a
classification
When you classify your data, you
can either use one of the standard
classification schemes ArcMap
provides or create custom classes
based on class ranges you
specify. If you choose to let
ArcMap classify the data, simply
choose the classification scheme
you want and set the number of
classes. If you want to define
your own classes, you can
manually add class breaks and set
class ranges that are appropriate
for your data. Alternatively, you
can start with one of the standard
classifications and make adjustments as needed.
Why set class ranges manually?
There may already be certain
standards or guidelines for
mapping your data. For example,
temperature maps are often
displayed with 10 degree
temperature bands. Or you might
want to emphasize features with
particular values, for example,
those above or below a threshold
value that determines whether
some action will occur. Whatever
your reason, make sure you
clearly specify what the classes
mean on the map.
2
Setting a standard
classification method
1. In the table of contents, rightclick the layer that shows a
quantitative value for which
you want to change the
classification.
4
3
2. Click the Symbology tab.
3. Click Quantities.
You should see the current
classification.
4. Click Classify.
5. Click the Method dropdown
arrow and click the classification method you want.
8
6. Click the Classes dropdown
arrow and click the number of
classes you want to display.
7. Click OK on the Classification
dialog box.
8. Click OK on the Layer
Properties dialog box.
6
5
7
SYMBOLIZING
ch6.p65
153
YOUR DATA
153
12/04/2000, 12:14 PM
Inserting your own class
break and setting a range
1. In the table of contents, rightclick the layer you want to set
class breaks for.
You should see the current
classification.
2. Click the Range you want to
edit.
Make sure to click the Range,
not the Label.
3. Type a new value. This sets
the upper value of the range.
4. Click OK.
2
Deleting a class break
Tip
Seeing more data values
plotted on the histogram
Increase the number of columns
shown to see more data values in
the histogram.
1. Click Classify from the
Symbology tab of the Layer
Properties dialog.
2. Click on the class break you
want to delete.
The selected break is
highlighted.
3
3. Right-click over the histogram
and click Delete Break.
154
ch6.p65
4
USING ARCMAP
154
12/07/2000, 8:30 AM
See Also
For more information on building
query expressions, see Chapter 13,
‘Querying maps’.
2
Excluding features from
the classification
1. Click Classify from the
Symbology tab of the Layer
Properties dialog.
2. Click Exclusion.
3. Double-click the field you’re
using to draw the layer.
4. Double-click an operator.
5. Double-click the value you
want to exclude.
If you don’t see the value in
the list, click the Complete
List button.
6. Click OK to execute the
expression and exclude
values.
4
5
3
6
SYMBOLIZING
ch6.p65
155
YOUR DATA
155
12/04/2000, 12:14 PM
Drawing features
to show multiple
attributes
Geographic data usually has a
number of different attributes
that describe the features it
contains. While you’ll commonly
use one of the attributes to
symbolize the data—for example,
show categories or quantities—
you may sometimes want to use
more than one. For example, you
might display a road network
using two attributes: one
representing the type of road and
the other representing the traffic
volume along it. In this case, you
could use different line colors to
represent the different types of
roads and also vary the line width
to indicate traffic volume along
each road.
When you symbolize your data
using more than one attribute,
you create a multivariate display.
Symbolizing your data this way
can effectively display more
information about the data;
however, it can also make your
map more difficult to interpret.
Sometimes it might be better to
create two separate displays than
to try to display the information
together.
2
Drawing a layer to show
both categories and
quantities
1. In the table of contents, rightclick the layer you want to
draw showing multiple
attributes and click Properties.
4
5
3
2. Click the Symbology tab.
3. Click Multiple Attributes.
ArcMap automatically selects
the Quantity by category
option.
4. Click the first Value Fields
dropdown arrow and click the
field that contains the values
you want to map.
5. Click the Color Scheme
dropdown arrow and click a
color scheme.
6
Q
7
8
6. Click Add All Values.
7. Click Symbol Size or Color
Ramp, depending on how you
want to symbolize the
quantitative value. This
example shows Symbol Size.
8. Click the Value dropdown
arrow and click the quantitative value you want to map.
Set other options as described in ‘Drawing features
to show quantities like counts
or amounts’.
9
9. Click OK.
10.Click OK.
156
ch6.p65
USING ARCMAP
156
12/04/2000, 12:15 PM
Drawing features
with charts
Pie charts, bar charts, and
stacked bar charts can present
large amounts of quantitative
data in an eye-catching fashion.
For example, if you’re mapping
population by county, you can
use a pie chart to show the
percentage of the population by
ethnic group for each county.
Generally, you’ll draw a layer
with charts when your layer has
a number of related numeric
attributes that you wish to
compare. Use pie charts if you
want to show how much of the
total amount each category takes
up. Use bar charts to show
relative amounts, rather than a
proportion of a total.
Tip
2 5
Drawing pie charts
1. In the table of contents, rightclick the layer you want to
draw showing quantitative
values and click Properties.
2. Click the Symbology tab.
3. Click Charts and click Pie.
4. Click one or more fields
under Field Selection that
contain the quantitative
values that you want to map.
3
4
7
5. Click the arrow button to add
fields to the field list.
6. Click the Color Scheme
dropdown arrow and click the
colors you want to use.
E8
You can double-click an
individual symbol in the list to
change its properties.
7. Check the box to prevent the
charts from overlapping.
6
9
8. Click Size.
Charting negative values
Avoid using pie or stacked bar
charts with data containing
negative values.
9. Click the Variation Type you
want.
Q
You can either draw all pies
the same size or vary the size
based on the sum of the
attributes or a particular
attribute value.
10.Type in a size or click the
arrows to set the size.
W
11. Click OK.
12.Click OK.
SYMBOLIZING
ch6.p65
157
YOUR DATA
157
12/04/2000, 12:15 PM
2 5
Drawing bar and column
charts
1. In the table of contents, rightclick the layer you want to
draw showing quantitative
values and click Properties.
2. Click the Symbology tab.
3. Click Charts and click Bar/
Column.
4. Click one or more fields
under Field Selection that
contain the quantitative
values that you want to map.
3
4
7
5. Click the arrow button to add
fields to the field list.
W8
6. Click the Color Scheme
dropdown arrow and click the
colors you want to use.
You can double-click an
individual symbol in the list to
change its properties.
6
Q
7. Check the box to prevent the
charts from overlapping.
8. Click Size.
Click Properties to
switch between bars
and columns.
9. Type in a maximum length or
click the arrows to set the
length.
10.Click OK.
11. Click OK.
9
158
ch6.p65
USING ARCMAP
158
12/04/2000, 12:15 PM
2 5
Drawing stacked charts
1. In the table of contents, rightclick the layer you want to
draw showing quantitative
values and click Properties.
2. Click the Symbology tab.
3. Click Charts and click
Stacked.
4. Click one or more fields
under Field Selection that
contain the quantitative
values that you want to map.
3
4
7
5. Click the arrow button to add
fields to the field list.
6. Click the Color Scheme
dropdown arrow and click the
colors you want to use.
W8
You can double-click an
individual symbol in the list to
change its properties.
6
Q
7. Check the box to prevent the
charts from overlapping.
8. Click Size.
9. Type in a maximum length or
click the arrows to set the
length.
Click Properties to
switch between bars
and columns.
10.Click OK.
11. Click OK.
SYMBOLIZING
ch6.p65
9
159
YOUR DATA
159
12/04/2000, 12:15 PM
Drawing TINs as
surfaces
TINs represent continuous
surfaces such as terrain elevation
or temperature gradient. Typically, you display a TIN using
color-shaded relief. This lets you
easily see the ridges, valleys, and
hillsides and their respective
heights. Seeing the data this way
can help explain why other map
features are where they are.
You can display any one of three
surface characteristics—slope,
aspect, and elevation—on your
map and even simulate shaded
relief.
Geographic features that cross
the surface—such as a river,
road, or shoreline—can be
explicitly represented in a TIN
with a breakline. These features
form the edges of triangles and
therefore influence the surface at
their location. Since the underlying triangulation defines the
surface, you might want to take a
closer look at it. You can also
display the internal structure of a
TIN—for example, nodes and
breaklines—independently or on
top of the shaded relief display.
2
Drawing a color-shaded
relief surface
1. In the table of contents, rightclick the TIN layer that you
want to draw and click
Properties.
3
2. Click the Symbology tab.
By default, ArcMap displays
the face elevation and
breakline edges of the TIN.
5
3. Click an entry in the list to see
its symbolization properties.
4. Modify the symbolization
properties as necessary. For
example, set a new color
ramp or change the number
of classes.
5. Click the Add button to draw
additional elements of the
TIN—for example, nodes.
6. Click the renderer that
represents the TIN feature
you want to draw.
6
7. Click Add.
7
8. Click Dismiss when you are
finished adding renderers.
8
The list will update to show
what you want to draw. u
160
ch6.p65
4
USING ARCMAP
160
12/04/2000, 12:16 PM
Tip
9. Click an element in the list.
How are slope and aspect
measured?
Slope values range between 0 and
90 degrees, where 0 indicates no
slope. Aspect is also measured in
degrees. North is 0 degrees, east is
90 degrees, south is 180 degrees,
and west is 270 degrees.
10. Click the Up or Down arrow
to change its draw order.
The TIN features at the top of
the list will draw on top of
those below them.
9
11. Click OK.
Q
W
SYMBOLIZING
ch6.p65
161
YOUR DATA
161
12/04/2000, 12:16 PM
Drawing CAD
layers
You can display CAD drawings
on your map just like other data
types. You can decide which
CAD layers to draw and how to
draw the entities on the layer.
Depending on how you added the
CAD data to your map, you have
two display options:
•
•
If you added the CAD
drawing file for display only,
you can only choose which
CAD layers to show or hide.
ArcMap draws all entities
according to the color
specified in the drawing file.
You can’t override this
drawing behavior.
Displaying a CAD
drawing file
2
1. In the table of contents, rightclick the CAD drawing layer
and click Properties.
2. Click the Display tab.
3. Click and drag the sliders to
adjust the CAD display.
3
4. Click the Drawing Layers tab.
5. Check the CAD layers that
you want to display.
6. Click OK.
4
If you added the CAD
drawing as features—point,
line, or polygon—because
you are interested in using the
data for geographic analysis,
you have access to all the
symbolization options as
other feature layers. For
example, you can draw the
polygon entities with a single
symbol or classified by a
unique value.
5
6
162
ch6.p65
USING ARCMAP
162
12/04/2000, 12:17 PM
See Also
For more information on symbolizing the features in a CAD dataset,
see ‘Drawing features to show
categories like names or types’ in
this chapter.
Tip
Adjusting transparency
You can also use the Effects
toolbar to adjust the transparency
of CAD layers.
2
Drawing CAD features as
points, lines, or polygons
1. In the table of contents, rightclick the CAD dataset and
click Properties.
2. Click the Symbology tab.
3
The drawing options available to you are the same as
other feature layers.
3. Modify the drawing properties
as necessary.
See the previous topics in
this chapter for more detailed
instructions.
4. Click the Drawing Layers tab.
5. Check the CAD layers that
you want to display.
4
6. Click OK.
5
6
SYMBOLIZING
ch6.p65
163
YOUR DATA
163
12/04/2000, 12:17 PM
Advanced
symbolization
ArcMap provides a few other
tools that let you control how
layers draw. You can:
•
Draw layers transparently.
•
Set a reference scale for
symbols so they’ll, for
example, get larger as you
zoom in on the map.
•
Order the drawing sequence
of multilevel road networks
with complex symbology.
Drawing a layer
transparently
1. Click the View menu, point to
Toolbars, and click Effects.
3
2
The Effects toolbar appears.
4
2. Click the Layer dropdown
arrow and click the layer you
want to adjust.
3. Click Adjust Transparency.
4. Drag the slider bar to adjust
the transparency.
Transparency is especially useful
for drawing raster layers over
other layers on your map,
allowing you to see the raster
layer while still viewing underlying features.
When you set a reference scale,
symbols and text will appear
larger as you zoom in on your
data frame and smaller as you
zoom out on your data frame. So
for example, text labels will get
larger if you zoom in to a scale
that is larger than the reference
scale.
Fire station layer before (left) and after adjusting transparency.
The current scale of the data
frame is used as the reference
scale to which all symbols and
text in the data frame will be
made relative. Setting a reference
scale is like “freezing” the
symbol and text sizes used in
your data frame so that the way u
164
ch6.p65
USING ARCMAP
164
12/04/2000, 12:17 PM
they look at the reference scale is
maintained at all scales.
One reason to set a reference
scale is if you want the detail in
your data frame to look the same
onscreen in Data view as it will
when you print it out. Let’s say
you are creating a map for
publication that will be printed
out at a scale of 1:25,000. If you
set your data frame’s scale to be
1:25,000 and then choose Set
Reference Scale, the symbols and
text sizes in your data frame will
appear on-screen at the same size
in relation to each other that they
will have in your printed map.
When a reference scale is set, all
layers (except for raster layers) in
the current data frame will have
their symbols scaled relative to
the reference scale. However, you
can disable scaling for individual
layers: double-click the layer, go
to the Display tab, and uncheck
“Scale symbols when a reference
scale is set.”
Setting a reference scale
for symbols
1. Set the scale of the data
frame to the scale you want
to use as the reference scale.
1
2. Right-click the data frame in
the table of contents and click
Set Reference Scale.
2
Clearing a reference
scale
1. Right-click the data frame in
the table of contents and click
Clear Reference Scale.
With (left) and without (right) a reference scale set.
SYMBOLIZING
ch6.p65
165
YOUR DATA
165
12/04/2000, 12:17 PM
Tip
What does Advanced
Drawing Options provide?
Use the Advanced Drawing
Options to order the drawing
sequence of multilevel road
networks with complex symbology.
You can drag and reorder the
drawing sequence, join features
drawn with the same multilayered
symbol, and merge features drawn
with a variety of multilayered
symbols.
Tip
Symbolizing your data
Symbolizing by unique values will
help when drawing layers with
complex intersecting features.
Arranging the drawing
order of complex
symbols and features
1. In the table of contents, rightclick a data frame and click
Advanced Drawing Options.
2. Check Draw using advanced
drawing options.
1
3. Click each symbol and set the
appropriate properties.
Use the pictures to help you
decide how you want the
symbols to interact as they
draw.
4. Click Apply to view your
changes.
5. Click OK.
2
3
4
5
166
ch6.p65
USING ARCMAP
166
12/04/2000, 12:18 PM